The flash memory for example utilizes a laminated gate structure made from tungsten/polysilicon (poly-Si) in order to lower the resistance of the gate electrode.
Polysilicon for example is used in the floating gate electrode layer, and a metallic material such as tungsten and the compounds is used in the control gate electrode layer.
As this laminated gate structure is made thinner and smaller, the interlayer leak currents can no longer be ignored.
Moreover, the leak current from the side wall can also no longer be ignored as the elements become smaller.
The polysilicon side wall of the laminated gate structure must be oxidized to suppress this leak current and to improve the electric characteristics.
However, when the polysilicon oxidized the side wall, the control electrode layer also becomes oxidized at the same time.
Oxidizing the control electrode layer raises the resistance of the gate electrode, and causes hair shaped crystals called whiskers to pierce through the adjacent film and develop to a point that destroys the semiconductor, causing lower flash memory performance and a lower production yield.
Substrate processing methods were therefore proposed that utilize so-called selective oxidation methods that utilize a gas containing oxygen and hydrogen to oxidize the polysilicon and that do not oxidize the control electrode made from metal. Refer for example to the patent document 1.    Patent Document 1: Japanese Patent Non-Examined Publication No. 2002-176051